In recent years, imaging optical devices represented by digital still cameras and digital video cameras (simply referred to as “digital cameras”, hereinafter) have spread rapidly. For example, a large number of such digital cameras are commercialized that have the number of recorded-image pixels greater than 5 million. Among these, digital cameras of reduced size and weight are desired in particular.
Further, recently, digital cameras are strongly desired that have a blur compensation function for compensating blur at the time of image shooting. Thus, simultaneous realization of the installation of a blur compensation function and the size and weight reduction is a large issue of development.
In the case of an imaging optical device for shooting a still image, in general, drive control is performed such that at least a part of the lens system is moved in a direction perpendicular to the optical axis so as to deflect the shooting view angle such as to cancel the deflection of the shooting view angle caused by blur. As a result, blur compensation is achieved.
When a blur compensation function is to be provided in a lens system, degradation need be avoided in the optical image formation performance when a part of lens units of the lens system is moved in a direction perpendicular to the optical axis. Then, in order that the avoidance of degradation is achieved in the optical image formation performance, the aberration of each lens unit in an isolated state need be compensated satisfactorily. This causes a tendency of size increase in the lens system.
As an example of a lens system having such a blur compensation function, the following lens systems are proposed (Japanese Laid-Open Patent Publication No. 2002-72086 and Japanese Laid-Open Patent Publication No. 2003-228001).
Each of the lens systems described in Japanese Laid-Open Patent Publication No. 2002-72086 and Japanese Laid-Open Patent Publication No. 2003-228001 is a zoom lens system, in order from the object side to the image side, comprises: a first lens unit having positive optical power; a second lens unit having negative optical power; a third lens unit having positive optical power; and a fourth lens unit having positive optical power. Then, the zoom lens system described in Japanese Laid-Open Patent Publication No. 2002-72086 has a blur compensation function of moving the entire third lens unit in a direction perpendicular to the optical axis. Further, in the zoom lens system described in Japanese Laid-Open Patent Publication No. 2003-228001, the third lens unit is divided into two. Then, a blur compensation function is provided such that one of the two lens units is moved in a direction perpendicular to the optical axis.
The zoom lens system described in Japanese Laid-Open Patent Publication No. 2002-72086 is a zoom lens system comprising a plurality of lens units, wherein magnification change is performed by changing an interval between individual lens units. Among the plurality of lens units, one lens unit moves in a direction perpendicular to the optical axis so as to serve as a blur compensation lens unit. Then, in each lens unit in the zoom lens system, for the purpose of satisfactory image formation performance in a range from a wide-angle limit to a telephoto limit, the aberration of each lens unit in an isolated state is compensated comparatively satisfactorily. This satisfactorily suits aberration compensation for achieving a blur compensation function. Accordingly, the zoom lens system described in Japanese Laid-Open Patent Publication No. 2002-72086 is provided with a blur compensation function without the necessity of a remarkable size increase.
Nevertheless, in the zoom lens system described in Japanese Laid-Open Patent Publication No. 2002-72086, the blur compensation lens unit is constructed from a large number of lens elements, and has a heavy mass. Thus, in order to achieve satisfactory blur compensation drive, the driving force of a blur compensation driving actuator need be increased. Then, when the driving force of the blur compensation driving actuator is increased as such, its volume is also increased. This causes a problem that size and weight reduction becomes difficult to be achieved in the entire imaging optical device.
Thus, in view of this problem, in the zoom lens system described in Japanese Laid-Open Patent Publication No. 2003-228001, one lens unit is divided into two, and then one of the two lens units serves as a blur compensation lens unit. By virtue of this, in the blur compensation lens unit, size and weight reduction is achieved, while reduction of the movement amplitude in a direction perpendicular to the optical axis is achieved. As a result, a comparatively small and light-weight imaging optical device is realized.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-72086    Patent Document 2: Japanese Laid-Open Patent Publication No. 2003-228001